Honestly, the only reason to add more elements is if the others are missing something.
And seeing as darkness, life, and light yet to have a "theme" for themselves, we'd actually need five new things.
(Aether == immortals. Air == dive. Darkness == Vampire? Steal? Death == Kill stuff. Earth == Burro. Entropy == Chaos. Fire == Glass cannon. Gravity == large HP stuff, plus momentum. Life == healing? Big creatures for cheap? Light == Healing? Good Shields? Time == Draw power. Water == Freeze)
Light - look at Hope, Luciferin, RoL and Nymph... to me its clear the theme of Light is Bioluminescence
Darkness - its the vampiric skill: nymph, stiletto, vampire, drain life, liquid shadow.
Life should be healing. It has heal, druidic staff, and bonds, but I dont feel its theme so strong like Light and Darkness ones.
And really, Air is surely not Dive. But I also failed to identify its theme.